1. Field of the Invention
The present invention relates to a sealing structure for sealing two members in a liquid-tight or air-tight fashion by using two kinds of sealing layers having different characteristics.
2. Description of Prior Art
Generally, as means for sealing two members from each other in a liquid-tight or air-tight fashion by inserting a synthetic resin, metal or paper gasket between them is widely employed.
However, where this kind of sealing structure is applied, for example, to the control valve unit of the automatic gear of an automobile, the use of a plurality of gaskets has been necessitated resulting in lowering the fabricability of the valve unit Further, there has arisen the problem that it is necessary to form a number of through holes in the gaskets in correspondence to oil paths which not only increases the manufacturing cost of the gaskets but also makes it unable to meet any possible design change or the like with ease.
In order to solve the above-described problem, there has been proposed a sealing structure which is economical and which has an excellent fabricability wherein a synthetic resin material or the like is printed on the mating surface of one of two members to be sealed so that a sealing portion is integrally formed on that member.
However, even in the case of the above-mentioned sealing structure, when a sealing portion made of a soft material is formed on the mating surface of one of two members to increase the sealing property, the sealing portion is abnormally deformed by bolt fastening so that both edges of the sealing portion come off from the mating surface while on the contrary, when a sealing portion made of a hard material is formed on that surface, the sealing property of the sealing portion lowers.
Accordingly, in Japanese Unexamined Patent Publication No.S62-249786, there is proposed a sealing structure in which a first sealing portion showing a comparatively non-compressibility is formed by printing on the mating surface of one of two members and a second sealing portion showing an elastic compressibility is formed by printing at a position near the first sealing portion in spaced apart and parallel relationship with the first sealing portion.
According to the sealing structure disclosed in the above-mentioned Japanese Unexamined patent Publication, the first sealing portion showing comparatively non-compressibility functions as a stopper for securing a gap between the two members so that the deformation of the second sealing portion showing elastic compressibility is controlled to thereby prevent the coming off of the second sealing portion due to its abnormal deformation. However, since the first and second sealing portions are arranged in parallel and spaced-apart relationship with each other, the problem have arisen that the width of the entire sealing portion becomes large so that it can not be applied to a unit having mating surfaces of small width such as a control valve.
Further, the above-mentioned sealing structure involves the problem that since the first and second sealing portions are bonded to the two members of different compositions, the use of materials for the first and second sealing portions is much restricted because of the necessity of securing the bonding power of the both members to a sufficient degree.